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Gerrymander map

This map, among the exhibits submitted with a lawsuit challenging Wisconsin's 2011 legislative map, shows the differences in legislative districts and representation under different scenarios, including a plan proposed in the lawsuit applied to 2012 election results.

The federal trial that will determine whether Wisconsin’s legislative district maps are lawful wrapped up this week in federal court. A three-judge panel is expected to make a decision in the case later this year.

The case centers around the validity of a new test for examining the parity of district lines. If the judges accept the test as a reliable metric of partisan balance, it could become a new standard for evaluating redistricting. This test — involving historical data sets of voter behavior correlated to the elected seats available — is called the “efficiency gap.” The test was developed by political scientists who have been working with the plaintiffs on their fight to repeal Wisconsin's maps.  

The plaintiffs in the case are 12 Democratic voters. The lead plaintiff is Bill Whitford, a retired University of Wisconsin Law School professor.

The efficiency gap is the centerpiece of the plaintiff’s case against the Republicans’ maps. It is promoted by its developers as the first quantitative model of its kind. They say it creates an objective, math-based judicial standard to evaluate whether the district lines drawn by the party in power are fair. The state has sought to undermine the validity of the model, saying in court this week it is not a “magic ball” in how it predicts fairness or election outcomes and said its numbers are not reliable.

Much of the witness testimony in the case looked at whether the conclusions reached by the efficiency gap are accurate. Debates over statistical relevance and computational approaches have ensued throughout the week. Other questions in the case include whether Wisconsin’s maps constitute gerrymandering, when district boundaries are changed to benefit a particular political party. 

In closing arguments Friday, Gerry Hebert, an attorney based in Virginia who is representing the plaintiffs, said Wisconsin's gerrymandered districts are "extreme," "unjustifiable" and strip some voters in the state of their electoral influence based on where they live. 

"The right to vote is fundamental, it’s our voice," he said. "It's not right to target people and harm them because of their political history."

Assistant Attorney General Brian Keenan defended the maps and said there is too much uncertainty to adopt the efficiency gap as a definitive judicial standard in evaluating new district boundaries and said the measurement doesn't accurately consider demographic and voting patterns in the state. 

“(It) just isn’t in touch with the underlying political reality of this country,” he said.

Here are some questions and answers useful to understanding the case.

What is the efficiency gap?

The gap represents the difference between political parties’ respective wasted votes in an election. The model considers a vote “wasted” if it:

1. Is cast for a losing candidate

2. Is cast for a winning candidate but that vote is in excess of what the candidate needs to win

Votes can be considered wasted as a result of districts that have been re-drawn for partisan advantage in the past, known as gerrymandering. Two techniques are commonly used:

1. Cracking — Spreading one party’s voters across multiple districts to dilute their voting power, denying the group representation in multiple districts

2. Packing — Concentrating one party’s voters in one district to limit their voting party to only one district, limiting its influence in other districts

Large numbers of votes commonly are cast for losing candidates as a result of cracking.

Likewise, excessive votes often are cast for winning candidates because of packing.

How is the efficiency gap calculated?

The efficiency gap combines the total of a district plan’s cracking and packing choices into a single number. It does this by breaking down the votes wasted and looking at which party wasted more, based on how the districts are drawn.

Who developed the efficiency gap? 

The efficiency gap was developed by Nicholas O. Stephanopoulos and Eric M. McGhee, both professors at the University of Chicago. Stephanopoulos has worked with the plaintiffs in the case who are contesting the Wisconsin maps.

What is partisan symmetry vs. proportional representation?

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Partisan symmetry is a standard for fairness in redistricting.

Partisan symmetry should be the goal of a redistricted map, say advocates of the efficiency gap test, where district lines are drawn that do not give one party an overwhelming partisan advantage. Votes cast to seats won may not be proportional, but instead districts are drawn so Democrats may have an advantage in one district, Republicans in another, but there is a balance across the map. 

Proportional representation is an electoral system where the make-up of the government is determined based on the number of votes each party received. The number of votes equals the number of seatsFor example, if a party wins 30 percent of the vote, it would get 30 percent of the seats.

This is an entirely different concept than partisan symmetry and is not a factor in the efficiency gap test. 

What is gerrymandering? And can it be unconstitutional?

Gerrymandering has been going on since 1812 in the U.S. But in 1986, the United States Supreme Court said the practice can be unconstitutional if it is severe enough.

In the 1986 case, Davis v. Bandemer, the high court upheld an Indiana law that redrew state districts but said that redistricting could be fought about in the courts and could be held unconstitutional if it was egregious enough.

Why are we talking about any of this?

Because re-drawing district lines has to happen, according to the law, every 10 years to keep pace with changes in population per the U.S. census. Legislative district lines matter because they have the potential to give one party a systemic advantage over another and can create an uneven electoral playing field. If you are a Republican voting in a densely Democratic district, your vote ostensibly matters less than if you live in a district that is made up equally of Democratic and Republican voters.

What’s special about Wisconsin’s redistricting case?

According to NYU’s Brennan Center for Justice: “The case is the first time in nearly three decades that partisan gerrymandering claims have survived a motion to dismiss in a trial court, and it will be a critical test for a proposed standard for evaluating partisan gerrymandering claims called the efficiency gap.”

Katelyn Ferral is The Cap Times' public affairs and investigative reporter. She joined the paper in 2015 and previously covered the energy industry for the Pittsburgh Tribune Review. She's also covered state politics and government in North Carolina.